Many processes in coatings have been developed for protecting metal substrates, and particularly carbon steel substrates, from both direct and electrochemical corrosion. Previously, metal substrates have been protected in varying degrees by applying organic and metal coatings such as phosphate, paint, plastic resins, zinc, lead, stainless steel, aluminum and the like. Heretofore, coated metal substrates have been utilized for storing and handling various combustible fuels. Numerous coatings have been utilized to provide chemical resistance for metal substrates. Chemical resistant coatings have been applied to tank interiors to protect against gasoline. However, with the development of alternative fuels, protecting such metal substrates from corrosion has become a much more challenging task.
One alternative fuel known as bio-diesel includes mono alkyl esters of long chain fatty acids derived from renewable biological sources. Bio-diesel can be manufactured from a variety of renewable sources such as vegetable oils, recycled cooking oils, animal fats, and tall oil from wood pulp waste. Common sources for bio-diesel include soybeans, rapeseed, jatropha nuts, coconuts, palm trees and the like. Based upon the feed stock, bio-diesel may be referred to as FAME fatty acid methyl ester (collective term for bio-diesel), for example, CME-coconut methyl ester, RME-rapeseed methyl ester, and SME soybean methyl ester. The designation Bxx is used to refer to the percentage of FAME blended with petroleum based diesel fuel. For example, B2 means that 2% FAME is blended with diesel fuel; B20 means that 20% FAME is blended with diesel fuel; and B100 means 100% FAME. Bio-diesel is of interest because it can be used to run existing diesel engines and can be distributed using current distribution infrastructure. Bio-diesel reduces hydrocarbon emissions and has positive performance attributes, for example increased cetane. The domestic production of bio-diesel provides energy security from a renewable source.
However, it has been discovered that bio-diesel fuel degradation products are extremely corrosive, and typical coatings used on combustible fuel storage and handling equipment are insufficient to prevent corrosion of the materials of construction of such equipment.